The normally staid North Carolina freshman was far from being the hero of his team's 75-73 win against No. 10 Kentucky, which had been billed as a battle of great freshmen, but when UNC's veterans knocked down enough free throws to seal the huge win, there was no wiping the smile off his face.
"We definitely needed that win today," Barnes said.
Tyler Zeller set a new career high with 27 points, including six big free throws in the final 81 seconds, and helped Carolina to a 34-14 advantage in points in the paint.
He also had career highs in rebounds (11) and blocks (5).
Point guard Larry Drew II, while not making a huge mark in the box score, was crucial in keeping the Tar Heels calm and collected at both ends of the floor in a game with 17 ties and 15 lead changes.
He also hit a pair of crucial free throws with 21 seconds to go.
"He played phenomenal," Zeller said. "He was under control the whole game. He played his role very, very well. I think he did a great job of running the team."
The Tar Heels (5-3) overcame a six-point deficit in the second half and rallied in a back-and-forth finish to get a win the team desperately needed to avoid a collapse of confidence.
"I've said all along, I really believe this team is going to be a really good basketball team," UNC coach Roy Williams said. "We just have to have some breakthroughs."
Count this game as a huge one.
After losing on the road at Illinois, the Tar Heels were in danger of falling to .500 if they lost to the Wildcats (5-2), not to mention losing some belief that they could win a big game against a ranked team.
So after returning from that road trip, they had a team meeting that lasted longer than an hour. The discussion centered around playing with more passion, energy and emotion.
Obviously, the message resonated, as the energy and enthusiasm was there for Carolina, especially in the final minutes with the momentum of their season hanging in the balance.
"It's going to be great for us, I think," Zeller said. "Obviously, we can't get content with just winning one. We have to continue to grow, continue to build on it. But it does show us and give us the confidence that we can beat this caliber of team and we are this caliber of a team."
With Kentucky's lack of size, it was no shock that Zeller quickly became Carolina's go-to option in the second half. Nor was it a surprise that four Wildcats fouled out, three of whom were forwards.
"Tonight was my night to be able to step up," Zeller said.
The only Tar Heels in double figures besides Zeller were Barnes (12 points) and John Henson (13 points).
But the lone point scored by that duo in the second half was a free throw by Henson that gave UNC a one-point lead with three minutes to go, setting up the back-and-forth lead changes down the stretch.
In the first half, Barnes was holding up his end of the bargain in the showdown between hyped-up freshmen.
After Carolina fell behind by eight, Barnes scored seven straight points, including a 3-pointer and an emphatic put-back jam, that helped the Tar Heels rally and retake the lead.
Kentucky's freshmen got off to an even quicker start than Barnes, with Brandon Knight and Doron Lamb combining for 24 first-half points.
But Barnes had the last laugh - not to mention that big smile - despite being shut out of the scoring column after the break and forcing things at times in the second half.
"At the end of the day, we won the game, so I don't care about matchups at this point," Barnes said.
Indeed, it was a win that could very well turn the Tar Heels' season around.
That's why Williams was glad to see a smile not just on Barnes' face but on everyone's after the huge win.
"I hope it'll be very important," Williams said. "The scene in our locker room after the game was a fun time. Hopefully, they'll realize what it takes to get there again."